Cytokines, growth factors and miRNA come up constantly in regenerative science. Anyone learning about the field, or about the Regenerative Protein Array (RPA) by Genesis Regenerative, will run into all three. They're often lumped together as if they were one family, but they aren't. Two are proteins. The third, miRNA, is a short strand of RNA that works in a completely different way.

Cytokines help coordinate the immune system. They're signaling proteins that cells release to start, sustain and wind down immune responses. Many cytokines work by binding to receptors on a cell's surface. That switches on enzymes inside the cell and sets off a chain of signals that reaches the nucleus, where genes are turned up or down. A single cytokine may have very different effects depending on which cell receives it. That flexibility is useful in the body, but it makes cytokines hard to work with precisely.

Growth factors are also proteins, and the line between them and cytokines is blurry. In general, growth factors are the messengers tied to building and maintaining tissue. They bind to receptors on target cells and influence whether those cells divide, move, specialize or survive. Two well-known examples are VEGF, which helps form new blood vessels, and PDGF, which helps recruit supporting cells. The same growth factor may act differently depending on timing, amount and which cells receive it.

miRNA works differently. MicroRNAs are tiny strands of RNA, about 22 building blocks long. They don't carry instructions for making a protein. Instead, they attach to messenger RNA, the cell's working copy of a gene, and reduce how much of that protein gets made. Thousands of human genes are thought to be regulated this way. If cytokines and growth factors are messages arriving at a cell, miRNA works more like a volume knob on how strongly the cell responds.

The three also travel differently. Cytokines and growth factors are released into the space between cells. Unprotected miRNA breaks down quickly outside a cell, so it travels inside protective carriers can be protected carriers, such as protein complexes and extracellular vesicles. How much miRNA delivered this way contributes is still being studied. Recent measurements found that even common miRNAs often average well under one copy per vesicle, which means most vesicles carry none at all. Researchers are working to understand how much these small amounts actually do.

Put together, the three describe layers of one communication system: signals that coordinate, signals that guide growth and maintenance, and regulators that fine-tune the response inside the receiving cell.

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